The invention relates to a thrust vector control for aircraft with one or more jet engines with each of the jet engines having a hrust nozzle with an at least approximately round, size-adjustable exit cross-section. More specifically, the invention is directed to high-performance fighter planes having a ring rudder arranged in an axially spaced position rearwardly of each jet engine and movable about at least one pivot axis extending substantially perpendicular to the longitudinal axis of the engine.
Based on currently applicable military principles, modern fighter or pursuit airplanes must meet requirements, in particular with regard to flight properties, which cannot be fulfilled with conventional technical solutions or only insufficiently so. These requirements include, among other things, the requirement of great maneuverability at extreme low flying speeds. Due to a low aproach velocity and unfavorable approach direction (i.e., a high angle of incidence), the effectiveness of control surfaces approached aerodynamically, i.e., by ambient air, is very low or no longer exists. The only meaningful alternative is, as a rule, a controlled deflection of the high-energy engine exhaust jet, of which VTOL aircraft are a particularly noteworthy example. But here, too, difficulties may arise, as for example, material problems due to the high exhaust temperature (to about 2000.about.K.), problems of strength and vibration due to the high flow velocities, negative effects on the engine throughput (m) due to backpressure effects, etc.
To avoid temperature problems, it is customary to provide a ring rudder having a cross-section which is larger in diameter than the diameter of the assooiated jet engine. The ring rudder is spaced axially behind the engine nozzle to envelope the exhaust jet with a cooling jacket of ambient air sucked in by an ejector effect. The cooling jacket of ambient air causes the rudder structure to remain at a relatively low temperature (max. about 300.about.C.). The cross-sectional form of the ring rudder is adapted to the nozzle form and is usually round or rectangular. Such an arrangement is shown, for example, in FIGS. 4 to 6 of DE-AS No. 11 00 385. The jet deflection reponse of such ejector ring rudders involves socalled dead zones, i.e., the rudder must first be deflected out by a certain angle before the exhaust jet is also deflected. The magnitude of this dead angle varies according to flight conditions and it varies especially--in the case of supersonic engines with adjustable nozzles--with the momentary size of the adjustable nozzle cross-section. This rather unpredictable behavior makes sensitive control and regulation practically impossible, thus ruling out utilization in high-performance aircraft. Alternatively the ring rudder could be made so small that it always lies at or in the nozzle jet. However, such a small-sized rudder and, possibly, also parts of the suspension and actuation mechanism would be continuously exposed to the high exhaust temperatures, to the detriment of useful life and reliability.
DE-OS No. 34 20 441 illustrates a jet control wherein a rudder cross with movable flaps (11 to 14) is arranged in an engine nozzle of fixed diameter. Upon failure or ineffectiveness of the aerodynamic rudders (4 to 8) the rudder cross permits movement about the pitch, yaw and roll axes, thereby increasing flight safety. The flaps (11 to 14) are preferably arranged so that they do not lie in the hottest core (17) of the exhaust jet. Yet the flaps and parts of their suspension are exposed to relatively high temperatures.
Tests have shown that while with plate or wing type rudders there is no occurrence of a dead angle effect in or behind the engine nozzle, only a relatively slight jet deflection (max. about 20.about.) is possible. This may suffice to increase flight safety, but does not provide a decisive improvement in the maneuverability of the aircraft.